"RFC 3021: Using 31-Bit Prefixes on IPv4 Point-to-Point Links" was published in December of 2000. Most systems have supported it for a long time, with Netgear (swearing under my breath) being the biggest outlier and straggler.
I think last time I used it there were a few bugs around redistribution. I tend to use private IPs, certainly for p2ps, so a /30 is fine